The present invention relates to a tool holder intended for chipforming machining of metallic workpieces, and especially to a clamping mechanism for clamping a cutting insert.
There exists a variety of tool holders for the mechanical clamping of cutting inserts such as rhombic, rhomboidic and triangular indexable inserts with equal angles all around the insert. The material used for such inserts is normally cemented carbide material or ceramic material.
A commonly used locking system for such indexable inserts includes a pin in the holder extending upwardly into the insert-receiving pocket to engage a hole in the insert located in said pocket, and means for forcing said pin to be subjected to a pivoting movement inwardly towards said holder. The forcing means is arranged to actuate the lower portion of said pin, thus urging both the pin and the insert inwards towards an upwardly extending wall formed on said holder rearwardly of said pocket. Such type of tool holder is disclosed in U.S. Pat. No. 3,314,126. The drawback of such holder, however, is that the forward nose portion of the cutting insert has a tendency of lifting off the shim plate located underneath said insert which sometimes can lead to insert failure.
It is also common to clamp the insert using a top clamp arm. However, a front portion of the clamp arm tends to wear too rapidly, especially as a result of being struck by chips created during machining operations.
In view thereof it is an object of the invention to provide a tool holder such that a clamp arm acting on the insert will ensure that the insert is pushed both downwards and inwards. At the same time, it is desirable that a front portion of the clamp acting on the insert can, in the best possible way, be protected against wear from the chips obtained during machining from the workpiece. It is also desirable to provide a tool holder that enables using both solid inserts and centrally apertured inserts in such holder.
All these desires can be fulfilled by providing said forcing means in the shape of a clamp arm actuated by a clamping screw which is provided with first and second contact surfaces. The first contact surface is provided on a forward protrusion of said clamp arm, and the second contact surface is provided on a rear protrusion of said clamp arm for engagement with a contact surface that is inclined in relation to the axis of said clamp screw. The forward protrusion of the clamp is received in a recess of a hard (preferably carbide) clamp plate that is interposed between the insert and the clamp arm, whereby the clamping forces are transmitted from the clamp arm to the insert through the clamp plate.